Lots of JW couples have used IVF. It’s no issue if you use your own sperm and eggs.
The WT has an issue if you use donor eggs or sperm, then they make a logic jump to “fornication”. Now of course if a married JW couple used either a donor egg or sperm and kept quiet about it, hard to prove, and they’d probably never be challenged on it.
In your scenario, a single JW sister would certainly have action taken. Either disfellowshipping, or maybe some public reproof and a marking talk if she claims ignorance or something.